Q1: Consensus

Is there a “consensus” in the science community on climate change?

Answer:

The consensus of scientific opinion is that the Earth’s climate is being affected by human activity. Despite claims made by some groups that there is not good evidence that the Earth’s climate is being affected by human activities, the scientific community overwhelmingly agrees that such evidence is clear, reliable and persuasive.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) said this:

“Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes (see Figure SPM.6 and Table SPM.1). This evidence for human influence has grown since AR4 (in 2007). It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. ” (1)

Q2: Natural warming

Couldn’t this be part of the natural warming and cooling of our planet?

Answer:

The Earth’s climate warms and cools naturally. The natural factors that effect these changes in climate occur over thousands, if not tens of thousands of years. The current change in climate has largely taken place in the last century, particularly in the last few decades.

Global temperatures indicate that the 20th century was very likely the warmest century of at least the past millennium, and the 1990’s were likely the warmest decade of this period. Although natural changes may contribute to the phenomenon, they do not match the very accelerated rate at which the Earth is warming.

Q3: Only a few degrees

Scientists predict that the Earth will warm only a few degrees. Why should we be concerned about such a small change?

Answer:

Scientists project a 1.4—5.8ºC rise in Global Average Surface Temperature (GAST) over the next century. While this may not seem large, it is.

The difference between present-day GAST and that of the last ice age (18,000 years ago) is only about 5ºC. This change was enough to melt ice sheets off continents and cause huge changes to ecosystems. A small change in GAST has a big impact on life on Earth.

Q4: Urban heat island effect

Answer:

As population centres (cities) grow in size, they also have a corresponding increase in average temperature. Scientists refer to this phenomenon as the “urban heat island effect” (UHIE).

Extensive research shows the UHIE can account for only a small amount (~0.05ºC at most) of the global warming observed over the past century. In fact, trends from rural and urban stations are very similar.

Furthermore, the ocean and borehole records, which are not affected at all by the UHIE, show similar amounts of warming over the last century.

Q5: Scientific uncertainty

I hear scientists talk about uncertainty. Does this mean they are uncertain that climate change is real or that it is due to human activity?

Answer:

Scientists are in overwhelming agreement that humans are causing climate change. The uncertainty lies in quantifying the exact amount of influence.

Uncertainty is expected in all scientific experiments and models. Having uncertainty does indicate doubt. And uncertainty does not make scientific results useless. It is the magnitude of uncertainty that is important. This term has been incorrectly interpreted and intentionally misused by some skeptics.

Q6: Extreme weather events

Are the recent extreme weather events caused by climate change?

Answer:

Given our knowledge of global warming and our changing climate, we can expect more extreme weather events and side-effects, including flooding and storms. But the attribution of any particular extreme weather event to climate change remains beyond the current limits of scientific capability.